Details please... what version of android are you running? Are you rooted, and if so are you stock or running a ROM? Have you made any changes, downloaded any new apps?
I will say I had to delete my gallery icon on my home screen and replace it after upgrading to 4.1.1
OK, 4.1.1 is jellybean. Do you have your gallery saved to a home screen? If so is the gallery icon a little green droid or does it look like the old gallery icon?
If it looks like a littler green droid, long press on the icon and drag it to "remove", then go to your app drawer and replace the gallery icon from there. It should work after that.
To check what version if android your on go to settings>about phone. Your android version is listed there. If you took the over the air update either yesterday or today you should be on 4.1.1 which is jelly bean.
Does it force close? Or does it open and is empty?
As mentioned, have you done anything recently?
Have you tried clearing data and/or cache on Gallery and/or Media storage [settings > apps > all (tab at top)]?
Are you rooted and/or running a custom ROM? If no, ignore the rest. If yes, which ROM? If yes, did you follow the install instructions for that ROM? Also, what Gapps did you use?